1. Field of the Invention
The invention describes proposals for intensifying and/or simplifying the separation of multicomponent mixtures of at least partly organic origin using a stream of carrier gas to simplify the removal of the more readily volatile constituents of the mixture. Accordingly, the principle behind the process according to the invention is based on purification steps which may be classified under the heading of "treatment with steam (steaming)". However, the working principle according to the invention differs from this in the choice of the carrier gas stream which is described in detail in the following in regard to its composition and the operating conditions applied and which is not formed by steam, but instead by a carrier gas of at least partly organic origin. Nevertheless, the measures known to the expert from steam distillation may be widely applied.
2. Discussion of Related Art
The principles of steam distillation for separating multicomponent mixtures and, in particular, for purifying useful materials or mixtures of useful materials of at least partly organic origin are part of established chemical knowledge, cf. for example L. Gattermann "Die Praxis des organischen Chemikers", 33rd Edition (1948), Walter De Gruyter & Co. Verlag, pages 26 to 28 and 252. The principles described herein for laboratory practice are used in various technical applications in such diverse forms that it is only possible here to refer briefly to a number of characteristic applications.
The purification of vegetable or animal fats and oils comprises a multistage treatment in which steaming of the prepurified material is usually carried out as the last stage. An important technical objective of this stage is deodorization of the prepurified material. Unwanted and, in particular, olfactorily troublesome impurities often present in traces only are separated from the useful material or mixture of useful materials by distillation with steam. However, this steaming stage may also be used as a distillation aid, for example to facilitate the removal of short-chain fatty acids from the natural fats and oils. The relevant literature is represented, for example, by "Ullmanns Enzyklopadie der technischen Chemie", 4th Edition, Vol. 11 (1976), pages 479-486; Kirk-Othmer "Encyclopedia of Chemical Technology", 3rd Edition, Vol. 9 (1980), pages 816-820 and E. Bernadini "Vegetable Oils and Fats Processing" in "Oilseeds, Oils and Fats", Vol. 11 (1983), InterstampaRome, Chapter VII, pages 221-251 (Deodorization of Fats and Oils). The industrial purification processes described herein using the principle of steam distillation or steaming operate in vacuo and at high temperatures. For example, steaming is carried out under a pressure of 2 to 30 mbar and at a temperature of 150.degree. to 290.degree. C. The amount of steam used and the treatment time are determined by the particular type of process selected. Batch processes, semicontinuous processes and continuous processes are known. Whatever the type of process, the steam is passed in finely dispersed form through the melted and flash-heated fat or oil. In semicontinuous and continuous processes, other aids may also be provided to enlarge the surface between the steam and the oil phase to be purified. Packed or filled columns in particular are described in this regard. In the column, the liquid to be purified is exposed to the steam passing through with a spread and, hence, enlarged surface.
Another typical industrially significant application for purification by steaming is the removal of residues based on ethylene oxide and/or propylene oxide from reaction products which have been produced by ethoxylation and/or propoxylation of organic compounds containing at least one active hydrogen atom. Compounds of this type are widely used, for example, as nonionic surfactants or as intermediate products for the production of anionic surfactant compounds. They are used, for example, in the field of detergents and cleaning formulations and also on a large scale in the field of cosmetics or pharmaceutical auxiliaries. From their production, the reaction products initially accumulating contain traces of ethylene oxide and/or propylene oxide and of unwanted secondary reaction products, such as dioxane. The removal of these residual materials from the alkoxylated derivatives is described in legislation and is an essential step of the production process. The steam distillation or rather steaming of the reaction products initially accumulating to remove the unwanted impurities is the process step industrially applied in practice, cf. for example EP-A1-0 283 862, DE-A1-34 47 867, U.S. Pat. No. 4,143,072 and the literature cited therein.
According to one modification of the above-described working principle, however, the useful materials or mixtures of useful materials to be purified may advantageously be heated in vacuo and at the same time concentrated by evaporation and purified by the principle of steam distillation. The use of additional, optionally superheated steam for this purpose is known from the prior art. If desired, the impurity-free products of relatively low water content thus obtained may be subsequently converted back into a water-containing preparation, cf. for example DE-A1 30 44 488 which describes a process for the production of ether sulfates of reduced dioxane content.
It is also known that the deodorization and/or removal of unwanted impurities can be carried out using non-condensable gas phases as a distillation aid. The preferred auxiliary for this purpose is gaseous nitrogen which may be used to facilitate removal of the more highly volatile constituents from mixtures, cf. for example JP-AS-5414/81. In this document, polyalkylene glycol derivatives (for example for use as emulsifiers, lubricating oils, starting materials for plastics, detergents, cosmetics and the like) are subjected to purification and deodorization by the introduction of gaseous nitrogen or steam into the liquid material to be purified at around 30 torr and at a temperature of 90.degree. to 100.degree. C. It has also recently been proposed to use non-condensable inert gases, especially nitrogen, instead of steam as a stripping aid in the above-mentioned deodorization of edible oils and/or fats, cf. for example EP-A2-015 739.
U.S. Pat. No. 4,443,634 describes a process for the purification of fatty alcohol polyglycol ethers, in which the material to be purified is sprayed into a chamber from which the impurities are removed in vaporous form. Corresponding mixtures containing less than 2% by weight of the impurities to be removed, based on the liquid starting material, are described as the material to be purified. The material to be purified is said to be sprayed in an inert atmosphere, the pressure having to be selected so that droplets between 50 and 1,000 .mu.m in diameter are formed. These droplets are said to be exposed to the inert gas atmosphere for a matter of seconds and then collected. Nitrogen, helium and argon are mentioned as inert gases. The impurities to be removed by this spray treatment are, in particular, ethylene oxide, propylene oxide, dioxane, water and alcohol. Spraying of the liquid phase into the space filled with inert gas may even be carried out several times in succession.
In their earlier German patent applications P 42 37 934.2 and P 43 07 115.5, applicants describe important improvements for purifying organic materials with superheated steam. The first of these two earlier patent applications describes a process for improving the purity and, in particular, color and odor of useful materials or mixtures of useful materials from the field of wetting agents, detergents and/or cleaning formulations (starting material), which is characterized in that an impurity-laden starting material is treated with superheated steam, bleaching agents optionally being used in the starting material to produce improvements in color. The impurity-laden starting material is preferably subjected to the treatment with superheated steam in fine-particle form and especially in admixture with water and, if desired, is at least partly dried at the same time. The treatment with superheated steam is best carried out in a spray zone and/or a fluidized bed.
The second of the earlier applications cited above describes a process for intensifying and/or accelerating the distillation-based separation of multicomponent mixtures of at least partly organic origin using a stream of steam to facilitate the removal of steam-volatile components of the starting material (steaming) which is characterized in that a starting material liquid under the treatment conditions is steamed in finely sprayed form. The treatment with steam is preferably carried out with steam superheated at the operating pressure. In one particularly important embodiment, the liquid phase to be purified is sprayed using a propellent gas. In one particularly advantageous embodiment, multicomponent spray nozzles are used. In the most important embodiments of this technical teaching, steam and, in particular, superheated steam is at least partly used as the propellent gas.
The disclosures of the two earlier German patent applications P 42 37 934.2 and P 43 07 115.5 cited above are hereby specifically included as part of the disclosure of the present invention. The principles described in those applications are also applicable to the teaching of the present invention as described in the following, the modification according to the invention being that a selected superheated vapor phase of at least partly organic origin is used instead of superheated steam as the gaseous entraining agent.
Before the teaching according to the invention is discussed in detail, applicants would first like to mention a totally different industrial application of the principles of steam distillation. It is known that, quite generally, difficult distillation-based separations can be made easier by applying the principle of steam distillation. For example, the removal of unreacted fatty alcohol components in the production of nonionic surfactants from the class of alkyl polyglycosides (APG) is described in EP-B-0 092 876 and later corresponding applications. Distillation of the APG-containing crude product is carried out in vacuo in a thin-layer evaporator. Removal of the free fatty alcohol to be distilled off can be promoted by exposing the starting material spread widely over the inner surface of the thin-layer evaporator to the stream of steam passing through with its enlarged surface.